Waduk means cistern, or a lake that formed from an embankment of a dam (actually i'm not sure 'cistern' is the right word so i'm going to use 'lake').

The place is being used as a recreational spot for people around the place. There's boat rentals, fishing pond, floating restaurants, room rentals (i just can't say hotel/motel when its just a wood chamber) and dike (again, i'm not sure 'dike' is what i meant, its when you put a 'fence' around a block of water and to grow fishes there). 

The majority of people that are coming here are fishing hobbyist. These people are bothered to come from a distant cities (such as Bandung) just to fish here. And when they do that, they may take a few days, that's why there's rooms and restaurants; in the midle of a lake.

I gotta say, its a nice place.

Its pretty cloudy because its just about to rain.